Referring to FIG. 1A, a Christmas tree 10 according to the prior art is illustrated in an elevational view. The Christmas tree 10 is attached atop conventional components of a wellhead known in the art. The tree 10 includes a tubing head 12, a tubing head adapter 16, a lower master gate valve 18, an upper master gate valve 20, and a flow tee 22. The flow tee 22 has a flow line gate valve 24 and a kill line gate valve 26. The gate valves 24 and 26 connect to additional components (e.g., piping) situated at a flow line elevation FE. The flow line elevation FE is measured from a production elevation, which can be measured from the top of the tubing head adapter 16 (e.g., production elevation PE) or measured from the bottom of the tubing head 12 (e.g., alternate production elevation PEALT). As shown in FIG. 1, the lower shut-off valve 18 and upper shut-off valve 20 are separate components.
The tree 10 is shown with a coil tubing assembly 40 attached atop the flow tee 22. To attach this assembly 40, an upper cap (not shown) that is initially attached atop the flow tree 22 is removed, and the coil tubing assembly 40 is attached to the flow tree 22. Then, coil tubing (also known as capillary) 30 is inserted through the vertical bore 28 that extends through the valves 18 and 20 of the tree 10. During operation, the coil tubing 30 is used to inject chemicals, to carry downhole sensors, or to perform a variety of other purposes. The coil tubing 30 typically has a diameter of ¼ or ⅜ inch.
As is recognized in the art, the coil tubing 30 when inserted in the vertical bore 28 can interfere with the valves 18 and 20 during an emergency shut off. For example, the coil tubing 30 may be severed by a closing shut off valve 18 or 20 so that communication between the vertical bore 28 of the tree 10 and the lower portions of the well (not shown). Severing the coil tubing 30 may cause damage to the valve 18 or 20 and could leave lower portions of the tubing 30 and any sensors or other components lost in the well.
One solution to the problems caused by running the coil tubing 30 through the vertical bore 28 and both valves 18 and 20 involves using a flanged coil tubing hanger between the valves 18 and 20. One example of such a prior art flanged coil tubing hanger 45 is illustrated in an elevational view in FIG. 1B. The flanged coil tubing hanger 45 is inserted between the lower master gate valve 18 and the upper master gate valve 20 to modify the Christmas tree arrangement 10 of FIG. 1A. The flanged coil tubing hanger 45 has flanged ends that connect to the flanged ends of the gate valves 18 and 20. By adding the flanged hanger 45, the resulting Christmas tree arrangement 11 of FIG. 1B has a new flow line elevation FENEW that is higher than the pre-existing flow line elevation FE. Thus, when the conventional Christmas tree arrangement 10 (as shown in FIG. 1A) is modified to add the flanged coil tubing hanger 45, additional components surrounding the modified Christmas tree arrangement 11 of FIG. 1B must be altered so that the flow lines will properly align with the gate valves 24 and 26 at the new flow line elevation FENEW. The need to modify surrounding components can increase costs and may require additional time for a crew to complete the work.
Another solution to the problems caused by running the coil tubing 30 through both valves 18 and 20 involves using a Y-body Christmas tree. One example of such a prior art Y-body Christmas tree 50 is illustrated in a perspective view and a partial cross-sectional view in FIGS. 2A and 2B, respectively. This Y-body Christmas tree 50 is disclosed in U.S. Pat. No. 6,851,478. The Y-body tree 50 has a body 60 formed as a single piece of steel that has a vertical bore 61 extending axially therethrough. The body 60 connects to a first shut-off valve 52 that is attached to the tubing head adapter 16 and the tubing head 12. The body 60 houses a second shut-off valve 62 for opening and closing the vertical bore 61. The body 60 also has gate valves 64 and 66 attached to an upper, flow tee portion 63 of the body 60 that communicate with the vertical bore 61. At the top of the vertical bore 61, the body 60 has a top cap 14 attached.
A coil tubing bore 70 formed in the body 60 connects to the vertical bore 61 below the upper shut-off valve 62 in the body 60. The coil tubing bore 70 extends upwardly at an angle from the vertical bore 61 so that coil tubing 80 can be fed through the coil tubing bore 70. A coil tubing head assembly 72 is attached to the coil tubing bore 70 so that the coil tubing 80 can be inserted and suspended through the lower shut-off valve 52 and not the upper shut-off valve 62.
The Y-body tree 50 can be added to an existing implementation such that the overall distance between the adapter 16 and the gate valves 64 and 66 at the upper, flow tee portion 63 is not changed. This has the advantage of not requiring additional labor to reconfigure other portions of an implementation. Despite the advantages provided by the Y-body tree 50, there are some disadvantages, as discussed below.
The Y-body tree 50 requires that the body 60 be intricately constructed and integrally formed, which can increase costs. In addition, the coil tubing bore 70 requires that the gate valves 64 and 66 be offset at 90-degrees from one another. In addition, if the upper shut-off valve 62 is closed and the lower shut-off valve 52 is not closed for whatever reason, the coil tubing bore 70 enables pressure from the vertical bore 61 to communicate above the upper shut-off valve 62, which may be undesirable. Furthermore, the coil tubing bore 70 may be prone to damage because it projects outwardly and upwardly from the majority of the Y-body tree 50. For example, the coil tubing bore 70 during operation and use can be exposed to damage caused by objects either falling or being moved around the Y-body tree 50.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
While the subject matter of the present disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. The figures and written description are not intended to limit the scope of the inventive concepts in any manner. Rather, the figures and written description are provided to illustrate the inventive concepts to a person skilled in the art by reference to particular embodiments, as required by 35 U.S.C. §112.